Variable voltage transformer



Oct. 27, 1964 N. N. BOJARSKI VARIABLE VOLTAGE TRANSFORMER Original Filed Nov. 8, 1957 3 Sheets-Sheet 2 O me i L! a 0 m m .l a 3 L INVENTOR. IVORBERT /V. 500A RSK/ @M,@@A,M @aa,

ATTORNEYS.

Oct. 27, 1964 N. N. BOJARSKI 3,154,756

VARIABLE VOLTAGE TRANSFORMER Original Filed Nov. 8, 1957 5 Sheets-Sheet 3 I10. 8 /O, FJG. 9

. INVENTOR. A oAwle' rAZ BOd/IRSK/ BY. @m M r @m,

ATTORNEYS.

United States Patent 3,154,756 VARHABLE VOLTAGE TRANSFURMER Norbert N. Bojarsid, Rochester, N.Y., assignor, by mesne assignments, to L. R. Power (1pm., Rochester, N.Y., a corporation of New York Continuation of abandoned application Ser. No. 695,394, Nov. 8, 1957. This application Feb. 8, 1962, Ser. No. 179 831 (Filed under Rule 47(1)) and 35 U811. 118) 6 Claims. (til. 336-133) This application relates generally to the electrical control art, and more particularly to a new and useful variable voltage transformer. This application is a continuation of Serial No. 695,394 filed Nov. 8, 1957, now abandoned.

It is an object of this invention to provide an efiicient, multi-purpose transformer adapted to produce an output voltage smoothly and continuously variable in infinitesimal increments, and which does not require brushes or other current-carrying moving parts.

Another object of this invention is to provide a variable voltage transformer wherein the primary reluctance is independent of the output voltage setting.

A variable voltage transformer constructed in accord with my invention is characterized by the provision of a transformer core having a primary and two secondary legs, a primary winding on the primary leg, a secondary winding on at least one of the secondary legs, and a magnetic armature section movable to divert primary flux from one of the secondary legs to the other thereof, thereby to vary the relative reluctance of the magnetic circuits comprising the secondary legs to vary the output voltage, the reluctance of the primary magnetic circuit being independent of the positional adjustment of the movable armature.

The foregoing and other objects, advantages and characterizing features of a variable voltage transformer constructed in accord with my invention will become clearly apparent from the ensuing detailed description of certain illustrative embodiments thereof, taken together with the accompanying drawings illustrating such embodiments wherein like reference numerals denote like parts throughout the various views and wherein:

FIG. 1 is a side elevational view of an illustrative embodiment of the transformer of this invention and its enclosing housing, with the cover member removed;

FIG. 2 is a sectional view thereof taken about on line 22 of FIG. 1;

FIG. 3 is a sectional view thereof taken about on line 33 of FIG. 2 and turned ninety degrees;

FIG. 4 is a generally diagrammatic view thereof illustrating its mode of operation;

FIG. 5 is a view corresponding to that of FIG. 4, but of another illustrative embodiment;

FIGS. 6 and 7 are fragmentary views thereof illustrating different positions of the movable section;

FIG. 8 is a perspective view of a modified armature construction;

FIG. 9 is a fragmentary sectional view of a transformer incorporating the movable armature sections of FIG. 8;

FIGS. 10 and 11 are fragmentary, generally diagrammatic views thereof illustrating different positions of the movable sections;

FIG. 12 is a perspective generally diagrammatic view of a transformer similar to that of FIGS. 1-4 but incorporating a modified armature construction corresponding to that of FIG. 8; and

FIG. 13 is a fragmentary, top plan view thereof, with a housing therefor shown in section.

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Referring now to the illustrative embodiment shown in FIGS. 1-4 of the accompanying drawing, a variable voltage transformer constructed in accord with my invention comprises a transformer core, generally designated 1, which preferably is of a laminated construction known in the art, and which is shown herein as being of generally E-shape having a center leg 2 and two outer legs 3 and 3. The laminations of core 1 are secured together, as by rivets 4, and are mounted in a housing 5 as by means of bolts 6 passing therethrough and threadedly engaging embossments '7 projecting from the rear wall 8 of housing 5. The front of housing 5 normally is closed by a cover 9, and ventilating openings 10 are provided through housing 5 and cover 9.

A primary winding 12 is placed on the center leg 2, having leads 13 and 14 adapted for connection to a source of exciting voltage. A pair of secondary windings 15 and 16 are placed on the two outer legs 3 and 3, respectively, these windings being oppositely wound and series connected through a common lead 17 to comprise a differential secondary winding 15, 16 having leads 18 and 19 adapted for connection to the load, not illustrated.

An armature, generally designated 21, bridges the free, outer end faces of core legs 2, 3 and 3'. Armature 21 also preferably is formed of stacked laminations held together as by a rivet 22, and is in working contact with the outer end faces of each of the three legs 2 and 3 thereby comprising a magnetic section across these legs completing a first circuit for magnetic flux including primary leg 2, armature section 21 and secondary leg 3, and a second circuit for magnetic fiux including primary leg 2, armature section 21 and secondary leg 3'.

In order to vary the net voltage induced in secondary windings 15, 16, I provide means for positionally adjusting or moving armature section 21 in the lengthwise direction thereof, in the plane of legs 2, 3 and 3' thereby to vary the relative reluctance of the magnetic circuits through secondary windings 15 and 16. To this end, armature 21 is confined for reciprocation in the direction of arrows 23 (FIG. 4), as by guide shoulders 24 on opposite sides thereof, which guide shoulders can depend from the top wall 25 of housing 5 and can be either integral therewith or formed separately thereof and attached thereto. For moving armature 21, I provide means which can comprise a rack 26 projecting from a bracket 27 fastened to armature 21 by a rivet 28, which rack meshes with a pinion 29. Pinion 29 is mounted on a shaft 30 journalled in a boss 32 carried on the rear wall 8 of housing 5, with shaft 30 extending therethrough for manipulation as by a knob 33.

Referring now to the schematic diagram of FIG. 4, the neutral position of armature 21 is shown in full lines. It will be noted that when in this position armature 21 is in working contact with the entire end face area of primary leg 2, and is in working contact with the inner half of the end face area of each secondary leg 3, 3. Therefore, all other factors being equal, the reluctance of each secondary magnetic circuit is the same, and because the secondary windings 15 and 16 are in opposition to each other the voltages induced therein buck each other and cancel out producing a zero net output voltage.

When armature 21 is moved to the extreme position illustrated in broken lines in FIG. 4, it is in working contact with the entire end face area of secondary leg 3 as well as of primary leg 2, and it is out of working contact with the end face of secondary leg 3, whereby the magnetic path containing leg 3 is of much less reluctance than the path containing leg 3' and the magnetic flux produced by primary winding 2 is diverted from leg 3' to leg 3. In other words, the relative reluctance of 3 the two secondary circuits is varied in a direction producing a much greater voltage induced in winding 15 than in winding 16, whereby there is produced a net maximum output voltage of one polarity.

Conversely, when armature Z1 is moved to its opposite extreme position illustrated by dot. and dash lines in FIG. 4, it is in working contact with the entire end face area of secondary leg 3' and is out of working contact with the end face of leg 3, thereby varying the relative secondary reluctance in the opposite direction to produce, inthe chosen example, an equal maximum net voltage of opposite polarity.

Obviously, armature section 21 can be moved to any position between the illustrated extremes to produce a net output voltage continuously variable between no voltage andv a maximum of. either polarity.

Thus, not only can the output voltage be readily and continuously varied by infinitesimal increments from one extreme to another, but those two extremes can encompass a reversal of polarity, and it is a particular feature of this invention that the primary reluctance is not affected by such variations in output voltage but is independent thereof; Primary leg 2 preferably has a cross sectional area equal to that of secondary leg 3, and also to that of secondary leg 3', all other things being equal, for maximum utilization of transformer capacity, and the total end face area of secondary legs 3 and 3' in working contact with armature 21 remains the same at all positions of armature 21 whereby the primary reluctance is independent of armature position. The primary leg end face has thee same area in working contact with armature 21 at all positions thereof.

A boss 35 depends from top wall 25 of housing 5 and bears against rack 26 to hold it in meshing engagement with pinion 29, and a spring element 36 secured to the housing top wall 25, as by a rivet 37, bears against the upper edge of armature 21' to hold it in working contact with the end faces of the core legs 2, 3 and 3'. Openings 38, surrounded by grommets 39 of insulating material are provided for passage of the primary and secondary leads 13, 14, 18 and 19 through the housing.

It is contemplated that the transformer of this invention will find wide utility wherever it is desired to vary the output voltage smoothly andcontinuously and without energy losses associated with rheostat and other conventional control elements. For example, it is thought that it would be highly useful in controlling the heating elements of electric stoves. In such cases, reversal of polarity probably would not be utilized, and the primary voltage could be used as a base. To this end, the transformer can be readily connected as an auto transformer, the primary being rapped into the secondary asby connecting leads l3 and 13, respectively, as indicated in broken lines at 39 (FIG. 4). By such means, variations between the two extremes would comprise variations above and below theprimary voltage as a base, with the output voltage being ofconstant polarity.

Also, the secondary windings 15 and 16 could be wound in. an. additive sense, instead of in opposition, if

they had an unequal number of turns, thereby producing an output voltage of constant polarity, variable between predetermined limits, and it is believed that this might.

find utility where only a relatively slight variation in output voltage. is desired. In another form, one of the secondary windings 15, 16 could be dispensed with, although its secondary leg would be retained, whereby the output voltage would beof constant polarity and variable from zero to the maximum rating of the retained secondary Winding. Of course, wherever two secondary windings are used, they need not have an equal number of turns.

In any case, the total secondary leg area in working contact with armature 21 remains constant with movement of the armature, whereby the primary reluctance is independent of armature movement. The total secondary reluctance remains constant, with variation in output voltage being obtained by varying the relative reluctance of the secondary magnetic circuits, and the primary leg area in working contact with armature 21 preferably is equal to the total secondary leg area in working contact therewith.

The transformer core I. obviously need not be fiat, nor must the movement of the armature section necessarily be linear. Thus, FIGS. 57 illustrate an embodiment of the invention wherein the armature movement is rotary.

In this form of the invention the basic arrangement and principle of operation remain the same. A core 101 having a primary leg 2% and a pair of secondary legs 3M and 3%, is provided, and primary winding 12 is placed on leg Ztih with secondary windings 15 and 16 placed on legs 3% and Zititi, respectively. The outer end face of primary leg 22% is concave and semicircular in form, and secondary legs 30% and 300' are extended, as at 316 and 31h, respectively, to present semi-circular,

concave end faces drawn on the same radius as the end face of leg 2%.

A movable section. 210 of generally cylindrical form having the radius of the primary and secondary leg end faces is arranged for working contact therewith. To this end, armature 21th is mounted on a shaft 212 for rotation about the axis thereof, and a section 211 is removed from armature 21d. Preferably, the magnetic section remaining in. armature Zllil is suflicient' to have simultaneous working contact with all of the endface of primary leg 2% and with one half the end face of each secondary leg 3%, 3%. Of course, armature 210 can be formed to this shape in any desired manner.

It is believed that the operation of this embodiment is clear from the foregoing and the detailed description of the previous embodiments. As illustrated in FIGS. 10 and Ill, in addition to rotating the armature to selectively divert the magnet flux as desired between'the two secondary legs, or entirely into one of them, it is possible to independently rotate the control elements 210' and 2169 to provide a still finer degree of control. The main section 216) is moved in the manner described in connection with the embodiment of FIGS. 5-7 to provide a relatively coarse adjustment, and the minor section Zltl" can be moved to a different position providing a fine adjustment modifying the main adjustment.

The embodiment illustrated in FIGS. l-4 can be similarly modified, as illustrated in FIGS. 12 and 13, to provide two armature sections 21' and 21" of different width. The sections Zll and 21 are independently movable, as by rack and pinion means, not illustrated, corresponding to those shown in FIGS. 13, and modified in a manner similar to that illustrated in FIG. 9, or by other suitable means, so that the larger main section 21' can be moved to provide a coarse adjustment, and the minor section 21" can be independently moved to modify the main adjustment and thereby achieve a finer degree of control.

Armature Zltl is adapted to be rotated about the axis of shaft 212, as by a control knob indicated in broken lines at 213. When in the extreme position illustrated in FIG. 5, armature 210 diverts all of the primary flux to secondary leg 310', as indicated by the arrow. When in its opposite extreme position illustrated in FIG. 6, armature 210 diverts the primary flux to secondary leg 310, and when in its neutral position illustrated in FIG. 7, the primary flux is divided equally between the secondary legs. and 16 will produce a net output voltage, which is smoothly and continuously variable, as discussed in connection with. the embodiment of FIGS. 1-4, and they. can be wound in opposition with either an equal or unequal number of turns, or in an additive sense with an unequal number of turns, or one thereof can be dispensed with, as previously discussed.

In any case, the total secondary end face area in work- The series connected secondary windings 15 ing contact with armature 210 remains constant, as does the primary end face area, whereby the primary reluctance is independent of variations in the output voltage, and the primary area in working contact with armature 210 preferably equals such total working secondary area.

Where a still finer adjustment in voltage ratio is desired, the movable diversion element or armature can be split or divided to comprise independently movable sections. Thus, referring for example to the embodiment illustrated in FIGS. 8-11, which corresponds generally to that of FIGS. 5-7, there is provided an armature comprising a first movable section 210 and a second section 210" movable relative thereto, the armature being split, to provide the two sections, in a plane containing the three legs of the core.

The sections 210' and 210 provide a total armature section corresponding to armature 210, whereby the total secondary end face area in working contact with the two armature sections remains constant, and the primary end face area in contact therewith also remains constant, as previously discussed. The relative thickness or volume of the sections 210' and 210" is determined by the degree of control which is desired. In other words, the two sections have dilferent cross sectional areas, in a ratio selected to provide the differential necessary to achieve the desired fineness of control. In operation, the larger section 210 can be mounted on shaft 212 for rotation by means of a knob 213, while the smaller section can be mounted on a coaxial shaft 212' for actuation by a coaxial knob 213'.

While only certain illustrative embodiments of my invention are described in detail herein, it will be appreciated that my invention is not necessarily limited to the details thereof but includes variations and modifications falling within the scope of the appended claims.

Having completely disclosed and described my invention, together with its mode of operation, what I claim as new is as follows:

1. A variable voltage transformer comprising, a transformer core having a primary leg and two secondary legs, a primary winding on said primary leg, a secondary winding on at least one of said secondary legs, and a magnetic armature coupling said primary leg with at least one of said secondary legs by working contact therewith, said armature being divided longitudinally into independent longitudinally movable sections each overlying said primary leg and portions of at least one secondary leg in working contact therewith, said armature being of such length that the composite total area of said secondary legs contacting each armature section and coupled thereby to said primary leg is constant for all working positions of said armature sections.

2. In a transformer as set forth in claim 1, resilient spring means abutting said armature and urging it into tight contact with said legs.

3. In a transformer as set forth in claim 1, separate secondary windings on said secondary legs, these windings being connected in series, with their voltages mutually in opposition.

4. in a transformer as set forth in claim 3, said secondary windings on said two secondary legs having different numbers of turns.

5. A variable voltage transformer comprising, a transformer core having a primary leg and two secondary legs, a primary winding on said primary leg, a secondary winding on at least one of said secondary legs, and a magnetic armature coupling said primary leg with at least one of said secondary legs by working contact therewith, said armature being divided longitudinally into independent longitudinally movable sections each overlying said primary leg and portions of at least one secondary leg in working contact therewith, said armature being of such length that the composite total area of said secondary legs contacting each armature section and coupled thereby to said primary leg is constant for all working positions of said armature sections, said armature including sections of mutually different cross-sectional area to provide adjustments of relatively coarser and finer degree for the same longitudinal movements of the latter sections.

6. A variable voltage transformer comprising, a transformer core having a primary leg and two secondary legs, a primary winding on said primary leg, a secondary winding on at least one of said secondary legs, and a magnetic armature coupling said primary leg with at least one of said secondary legs by working contact therewith, said armature being divided into independently movable sections each overlying said primary leg and portions of at least one secondary leg in working contact therewith, said armature being of such length that the composite total area of said secondary legs contacting each armature section and coupled thereby to said primary leg is constant for all working positions of said armature sections, said armature including sections of mutually different cross-sectional area to provide adjustments of relatively coarser and finer degree for the same movements of the sections.

References Cited by the Examiner UNITED STATES PATENTS JOHN F. BURNS, Primary Examiner. 

1. A VARIABLE VOLTAGE TRANSFORMER COMPRISING, A TRANSFORMER CORE HAVING A PRIMARY LEG AND TWO SECONDARY LEGS, A PRIMARY WINDING ON SAID PRIMARY LEG, A SECONDARY WINDING ON AT LEAST ONE OF SAID SECONDARY LEGS, AND A MAGNETIC ARMATURE COUPLING SAID PRIMARY LEG WITH AT LEAST ONE OF SAID SECONDARY LEGS BY WORKING CONTACT THEREWITH, SAID ARMATURE BEING DIVIDED LONGITUDINALLY INTO INDEPENDENT LONGITUDINALLY MOVABLE SECTIONS EACH OVERLYING SAID PRIMARY LEG AND PORTIONS OF AT LEAST ONE SECONDARY LEG IN WORKING CONTACT THEREWITH, SAID ARMATURE BEING OF SUCH LENGTH THAT THE COMPOSITE TOTAL AREA OF SAID SECONDARY LEGS CONTACTING EACH ARMATURE SECTION AND COUPLED THEREBY TO SAID PRIMARY LEG IS CONSTANT FOR ALL WORKING POSITIONS OF SAID ARMATURE SECTIONS. 